In recent years, vertical magnetic recording has been adopted by a magnetic disk drive to increase the recording density and capacity of the device or to achieve miniaturization of the device. In the magnetic disk drive of this type, a recording head for vertical magnetic recording is made to face a recording surface of the magnetic disk comprising a recording layer for vertical magnetic recording, a vertical field corresponding to the recording data is generated in a predetermined area on the magnetic disk by the recording head, and the data is thereby recorded.
The recording head comprises a main magnetic pole which has a tapered portion formed of a soft magnetic metal and generates a vertical field, a return magnetic pole which is opposed to the main magnetic pole with a write gap sandwiched between the return magnetic pole and the main magnetic pole, urges a magnetic flux from the main magnetic pole to return and forms a magnetic circuit together with the main magnetic pole, and a coil which excites the magnetic flux to the magnetic circuit formed by the main magnetic pole and the return magnetic pole and generates a record field.
The recording head configured as explained above comprises a spin torque oscillator (STO) in the write gap to attempt improvement of the recording power. An example of the spin torque oscillator is, for example, a high-frequency oscillator or a permeability regulator.
If a drive voltage is applied to STO, however, STO may generate heat and cause a fine element bump. Since this bump is fine, the bump amount can hardly be detected and measured, and high-accuracy correction of the bump amount is difficult. For this reason, if the element bump caused by STO drive is larger than expected, a problem arises that the element life may be remarkably degraded due to contact with an abnormal protrusion of the recording medium.
The problem to be solved by the embodiments is to provide a magnetic disk drive and a recording head control method capable of suppressing element bump caused by the STO drive and implementing improvement of the recording density.
Each of FIG. 9A and FIG. 9B is a characteristic graph showing element resistance change of STO to explain element life improvement effect resulting from application of the First Embodiment.
FIG. 10 is a flowchart for forming a corrected heater power value setting table for an STO voltage in Second Embodiment.
FIG. 11 is a characteristic graph showing a relationship between a heater power reduction amount at the STO voltage and an average track amplitude in the Second Embodiment.